Generally speaking, the present invention relates to a solid-state timed switching circuit which comprises in combination a power switching means, a single delay timing means which is connected to the power supply means and provides a time delay before power is turned on through a diode and triac to a function timing means, a function timing means which is connected to the delay timing means for timing an operational sequence for predetermined times, a power turn-off means which is connected directly to the function timing means to de-energize the power switching means without delay at the conclusion of the timing cycle of the function timing means, and an alarm timing means which is responsive to the power turn-off means providing an audible alarm at the conclusion of the timing cycle of the function timing means.
The present invention pertains to timed switching circuits and more particularly to a delay timed switching circuit which provides a delayed start to a timed operational sequence and includes solid-state switching devices. The present invention is a new combination which includes a timer for an appliance as disclosed in Schmidgall U.S. Pat. No. 3,767,937 dated Oct. 23, 1973, a timer switch as disclosed in Scott U.S. Pat. No. 3,846,748 dated Nov. 5, 1974, and a single delay timing means and is an improvement over the prior art because of its complete solid-state structure.
Because of the increasing variety of desired uses for timed switching circuits and the complexity of functions to be controlled thereby, it has become necessary that timed switching circuits be more compactly designed and at the same time possess improved timing accuracy and reliability. It has also become desirable in many applications to delay the start of timing cycles until some condition precedent to the proper function of the operational sequence has been completed. These requirements and others have become particularly desirable in the application of timed switching circuits to microwave ovens where the compact design of such units is coupled with the need to provide increased timing accuracy, short response time and delayed starts of the cooking system. Functions similar to these have previously been accomplished with electromechanical combinations of switches and other devices; however, such combinations are physically larger, have a longer response time and are less accurate than combinations of solid-state devices performing the same or similar functions.